1. Field of the Invention
The present invention relates generally to the field of downhole sampling analysis and in particular to obtaining an aliquot formation fluid micro sample down hole for rapid analysis on location to determine the quality of the down hole sample.
2. Summary of the Related Art
Earth formation fluids in a hydrocarbon producing well typically comprise a mixture of oil, gas, and water. The pressure, temperature and volume of formation fluids control the phase relation of these constituents. In a subsurface formation, high well fluid pressures often entrain gas within the oil above the bubble point pressure. When the pressure is reduced, the entrained or dissolved gaseous compounds separate from the liquid phase sample. The accurate measurement of pressure, temperature, and formation fluid composition from a particular well affects the commercial viability for producing fluids available from the well. The data also provides information regarding procedures for maximizing the completion and production of the respective hydrocarbon reservoir.
Certain techniques analyze the well fluids downhole in the well bore. U.S. Pat. No. 6,467,544 to Brown, et al. describes a sample chamber having a slidably disposed piston to define a sample cavity on one side of the piston and a buffer cavity on the other side of the piston. U.S. Pat. No. 5,361,839 to Griffith et al. (1993) disclosed a transducer for generating an output representative of fluid sample characteristics downhole in a wellbore. U.S. Pat. No. 5,329,811 to Schultz et al. (I 994) disclosed an apparatus and method for assessing pressure and volume data for a downhole well fluid sample.
Other techniques capture a well fluid sample for retrieval to the surface. U.S. Pat. No. 4,583,595 to Czenichow et al. (1986) disclosed a piston actuated mechanism for capturing a well fluid sample. U.S. Pat. No. 4,721,157 to Berzin (1988) disclosed a shifting valve sleeve for capturing a well fluid sample in a chamber. U.S. Pat. No. 4,766,955 to Petermann (1988) disclosed a piston engaged with a control valve for capturing a well fluid sample, and U.S. Pat. No. 4,903,765 to Zunkel (1990) disclosed a time-delayed well fluid sampler. U.S. Pat. No. 5,009,100 to Gruber et al. (1991) disclosed a wireline sampler for collecting a well fluid sample from a selected wellbore depth. U.S. Pat. No. 5,240,072 to Schultz et al. (1993) disclosed a multiple sample annulus pressure responsive sampler for permitting well fluid sample collection at different time and depth intervals, and U.S. Pat. No. 5,322,120 to Be et al. (1994) disclosed an electrically actuated hydraulic system for collecting well fluid samples deep in a wellbore.
Temperatures downhole in a deep wellbore often exceed 300 degrees F. When a hot formation fluid sample is retrieved to the surface at 70 degrees F, the resulting drop in temperature causes the formation fluid sample to contract. If the volume of the sample is unchanged, such contraction substantially reduces the sample pressure. A pressure drop causes changes in the situ formation fluid parameters, and can permit phase separation between liquids and gases entrained within the formation fluid sample. Phase separation significantly changes the formation fluid characteristics, and reduces the ability to evaluate the actual properties of the formation fluid.
To overcome this limitation, various techniques have been developed to maintain pressure of the formation fluid sample. U.S. Pat. No. 5,337,822 to Massie et al. (1994) pressurized a formation fluid sample with a hydraulically driven piston powered by a high-pressure gas. Similarly, U.S. Pat. No. 5,662,166 to Shammai (1997) used a pressurized gas to charge the formation fluid sample. U.S. Pat. Nos. 5,303,775 (1994) and 5,377,755 (1995) to Michaels et al. disclosed a bi-directional, positive displacement pump for increasing the formation fluid sample pressure above the bubble point so that subsequent cooling did not reduce the fluid pressure below the bubble point.
Typically, sample tanks are transported to laboratories for analysis for determination of formation fluid properties based on the sample. The samples typically have to be transferred to a transportation tank, thus risking sample damage and spoilage due to pressure loss and formation of bubbles or asphaltene precipitation within the sample. Moreover, even if the sample is transferred successfully to the laboratory, it typically takes weeks or months to receive a full laboratory analysis of the sample. Thus there is a need for a rapid sample analysis system that provides accurate results and eliminates the risk of sample spoilage.